Method and apparatus for control and regulation of a vehicle chassis having an adjustable damper

ABSTRACT

The invention relates to a process and a device for suspension control on vehicles, in which the reference damping force (reference value) for at least one adjustable damper with flow-resistance-damped piston is calculated from at least one status variable and is used for actuating the damper. It is proposed for the use of a damper of simple design that the actual value of the piston speed (x ar ) of the damper is fed to the damper by means of a family of characteristic curves, taking into account the calculated reference damping force (F d  ref), for the purpose of setting its adjustable through-flow cross-section (q).

BACKGROUND OF THE INVENTION

The invention relates to a process for suspension control on vehicles,in which the reference damping force (reference value) for at least oneadjustable damper with flow-resistance-damped piston is calculated fromat least one status variable and used for actuating the damper.

Conventional suspensions have a so-called passive damping system, whichmeans that a damper is connected parallel to the respectively presentspring arrangement of a wheel and has, for example, a liquid-dampedpiston. An expulsion of liquid occurs by means of tensile or compressiveforces. In this case, the liquid passes through a through-flowcross-section.

In a so-called semiactive suspension control, dampers are used whichhave a cylinder which is divided by a piston into two working spaces. Athrough-flow cross-section which can be controlled from outside isprovided for the pressure medium which can be expelled by the piston, sothat the damping properties (degrees of damping) can be adjusted.Depending on the vehicle state, the actual damping force is matched tothe current conditions by means of a control system by rapidly adjustingthe through-flow cross-section. In this way an improvement of thecomfort and of the driving safety of a vehicle can be achieved.

It is known to construct a vehicle control according to the Karnoppcontrol concept and to operate it with a semiactive special damper. Inthe Karnopp control concept, the damping force is adjustedproportionally to an absolute body speed. This so-called absolute bodyspeed is defined between an inertial system (fixed, independent system)and a point on the body of the vehicle. The aforesaid special damper haselectrically adjustable pressure control valves by means of which areference damping force, which is preset by the control circuit, can befed directly to the damper in order to adjust it. However, specialdampers of this kind are very costly.

SUMMARY OF THE INVENTION

In contrast with the above, the process according to the inventionhaving the features specified in the main claim has the advantage that asemiactive damper of simple construction in which there is simply anadjustable through-flow cross-section for the pressure medium which canbe expelled by the piston can be used. According to the invention, theactual value of the piston speed of the damper is fed to the damper bymeans of a family of characteristic curves, taking into account thereference damping force calculated by the control circuit, for thepurpose of setting its adjustable through-flow cross-section. Therefore,the family of characteristic curves assumes a matching function in thatthe output variable calculated in the suspension control system isconverted by the family of curves in such a way that a direct actuationof the through-flow cross-section of the damper is possible. Theaforementioned, known special damper with electrically adjustablepressure control valves can therefore be dispensed with.

In particular, it is provided that the calculated reference dampingforce is fed to the family of characteristic curves as an inputvariable. The reference damping force is preferably calculated accordingto the Karnopp control concept.

A further development of the invention proposes that the absolute bodyspeed which, as already mentioned above, occurs between the inertialsystem and the body of the vehicle, be calculated as status variable andthe reference damping force be determined from the said absolute vehiclebody speed and the relative piston speed (actual value) of the damperacting between the vehicle body and the suspension.

For the calculation of the reference damping force, either a digital orelse an analog computing circuit can be used.

According to a particularly preferred embodiment of the invention, thefamily of characteristic curves carries out a simulation of the damper,an actual damping force being supplied as output variable. This actualdamping force is connected, together with the calculated referencedamping force, to a controller for the purpose of forming a controldifferential, the output value of which controller is fed on the onehand to the damper as a measure of the through-flow cross-section to beset and on the other hand to the family of characteristic curves as aninput variable. Therefore, the family of characteristic curves receivesas input variables the piston speed (actual value) of the damper and thethrough-flow cross-section, or a voltage corresponding thereto, obtainedby calculation. By virtue of the aforesaid controller, the through-flowcross-section of the damper is adjusted by means of the referencevalue/actual value comparison of the damping force calculated inaccordance with the Karnopp control concept and of the damping forcesupplied by the family of characteristic curves until the referencevalue and actual value of the damping force coincide.

A voltage/through-flow cross-section converter is preferably connectedbetween the family of characteristic curves and the damper. Thisconverter sets the through-flow cross-section of the damper inaccordance with the associated control voltage.

The family of characteristic curves is preferably generatedelectronically. This can occur by means of digital or analog technology.

The invention also relates to a device for suspension control onvehicles, having a computing circuit which calculates from at least onestatus variable the reference damping force (reference value) for atleast one adjustable damper with flow-resistance-damped piston and feedsthis to the damper for the purpose of actuation, the actual value of thepiston speed of the damper being fed by means of a family ofcharacteristic curves to the damper, taking into account the calculatedreference damping force, for the purpose of setting its adjustablethrough-flow cross-section.

In particular, a sensor is provided which detects the piston travel ofthe damper and feeds it via a differentiator and a full-wave rectifierto a squaring element, the output value of which is multiplied by acontrol voltage corresponding to the through-flow cross-section for thepurpose of forming the actual damping force. A circuit design of thiskind can be implemented in a simple way in analog technology. The analogcircuit also provides for the vehicle body speed to be fed to aninverter which is changed over as a function of the sign of the pistonspeed and is connected via a half-wave rectifier to a summing point, towhich the output value of the full-wave rectifier is fed as a furtherinput variable, the output value of the summing point forming thereference damping force.

Particularly good results can be achieved with a suspension control inwhich each wheel of the vehicle is assigned an adjustable damper withassociated suspension control circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained below in greater detail with reference to thefigures, in which:

FIG. 1 shows a block circuit diagram of a device for suspension control,

FIG. 2 shows a further exemplary embodiment of a suspension control and

FIG. 3 shows a detailed block circuit diagram of the suspension controlaccording to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block circuit diagram of a suspension control with asemiactive damper 1, which has a piston 2 and an adjustable through-flowcross-section q. The adjustability of through-flow cross-section q isindicated by the oblique arrow which crosses the piston 2. The piston 2is provided with a piston rod 3, which cooperates with a sensor 4. Thelatter can be constructed, for example, as a potentiometer, so that therespectively set resistance value of the potentiometer corresponds tothe piston position in the damper. Therefore, a voltage whichcorresponds to the relative piston travel x_(ar) is available at theoutput 5 of the sensor 4. The relative piston travel is to be understoodas the compression travel between a wheel bearing part receiving a wheelof the vehicle and the body of the vehicle.

The sensor 4 is connected to a differentiator 6, which forms a relativepiston speed x_(ar) from the relative piston travel x_(ar). The pistonspeed x_(ar) is fed to a Karnopp circuit 7 and a storage and processingdevice 8 including mapped data representing a family of characteristiccurves, in each case as output variables. The Karnopp circuit 7 receivesan absolute vehicle body speed x_(a) as further input variable. Thisabsolute vehicle body speed is to be understood as the speed occurringbetween an inertial system and the body of the vehicle. The inertialsystem characterises an independent, stationary coordinate system.

The Karnopp circuit 7 calculates according to the known Karnopp controlconcept ("Skyhook") a reference damping force F_(d) ref from the inputvariable relative piston speed x_(ar) and vehicle body speed x_(a). Thisis to be understood as a force which is obtained by calculation and, onthe basis of the aforesaid Karnopp control concept, would have to bepresent at the semiactive damper 1.

The reference damping force F_(d) ref is fed, in addition to the alreadymentioned further input variable of the piston speed x_(ar), to storageand processing device 8, which calculates from these values thethrough-flow flow cross-section q in the case of the vehicle conditionsprevailing which would have to be set as control voltage. This controlvoltage is fed to a voltage/through-flow cross-section converter 9,which sets the through-flow cross-section q in accordance with the sizeof the control voltage.

In the exemplary embodiment of FIG. 2, identical parts are provided withidentical reference numerals. However, as a departure from the exemplaryembodiment of FIG. 1, the piston speed x_(ar) is fed to a storage andprocessing device 10 including mapped data representing a family ofcharacteristic curves which carries out a simulation of the semiactivedamper 1. An output 11 of storage and processing device 10 feeds anactual damping force F_(dact), obtained on the basis of the simulation,to a controller 12, which receives the reference damping force F_(d) refas further input variable from the Karnopp circuit 7 in order to form acontrol differential. At the output 13 of the controller 12, a controlvoltage corresponding to the through-flow cross-section q of the damper1 is available, which is fed on the one hand as input variable 14 tostorage and processing device 10 and on the other hand as input variable15 to the voltage/through-flow cross-section converter 9, which carriesout the setting of the through-flow cross-section q of the damper 1.

FIG. 3 shows a detailed block circuit diagram of an analog circuitaccording to the concept of the exemplary embodiment of FIG. 2. Thepiston travel x_(ar) is fed to the already mentioned differentiator 6,which can also contain a low-pass filter at the same time. The pistonspeed x_(ar) available at the output 16 of the differentiator 6 issupplied to a full-wave rectifier 17, at the output 18 of which thevalue of the piston speed x_(ar) is available. This value is supplied tostorage and processing device 10, specifically to the squaring element19. The output value of the squaring element 19 is connected to amultiplier 20 of storage and processing device 10, the output 21 ofwhich feeds the actual damping force F_(dact) to the controller 12.

The piston speed x_(ar) is also supplied to a sign comparator 22, whichreceives a reference potential B as further input variable. Thecomparator 22 tests whether the piston speed x_(ar) is positive ornegative with respect to the reference potential B. The output 23 of thesign comparator is connected to a controllable inverter 24, to which thevehicle body speed x_(a) is supplied as input variable. If the pistonspeed x_(ar) assumes a positive value with respect to the referencepotential B, the output 23 actuates the inverter 24 in such a way thatthe latter has the vehicle body speed x_(a) in unchanged form--that isto say not inverted--at its output 25. The inverter 24 inverts thevehicle body speed x_(a) if the piston speed x_(ar) assumes a negativevalue with respect to the reference potential B.

The output 25 of the inverter 24 is connected to a half-wave rectifier26, which allows through the positive values of the vehicle body speedx_(a). These are supplied to a summing point 27, which receives asfurther input variable the value of the piston speed x_(ar). The output28, at which the reference damping force F_(d) ref is available, isconnected to the controller 12. The control voltage for the through-flowcross-section q of the damper 1 is available at the output 13 of thecontroller, said control voltage being fed via an offset/limiter circuit29 to the multiplier 20 as input variable 30.

Since the damper 1 is simulated by storage and processing device 10 inthe exemplary embodiments of FIGS. 2 and 3, control only takes placewithin the electronic system, so that no mechanical delays occur. As aresult, the adjustment can occur very rapidly and without problems withhunting.

With the relatively simple design according to the invention, theKarnopp control principle can be implemented in a suspension control.This control concept can be combined in a simple manner with furthercontrols (e.g. carriage-dependent switching).

In particular, the electronic system upon which the solution accordingto the invention is based can be used directly "in situ", that is to sayat or in the damper 1. This applies equally to the necessary sensingsystem. To this extent, it is possible to realise a simple (alsoretrofittable) semiactive suspension control concept without separatesensors or control units having to be used. Preferably, each wheel ofthe vehicle is controlled individually, by means of which a clearimprovement in comfort and driving safety can be obtained.

What is claimed is:
 1. A method for at least one of control andregulation of a suspension system on a vehicle, said suspension systemincluding at least one adjustable damper having a piston and anadjustable flow cross section, said method comprising the stepsof:calculating a reference damping force for said damper, said referencedamping force dependent on at least one variable of state, said variableof state including an actual value of a velocity of a said piston;transmitting said actual value of said piston velocity to a storage andprocessing device (8, 10) including mapped data representingcharacteristic curves of an actual damping force (Fdact), said storageand processing device simulating said actual damping force (Fdact) insaid damper utilizing said mapped data; generating a control signal witha controller, said control signal dependent on said reference dampingforce (Fdref) and said actual damping force (Fdact); and transmittingsaid control signal to said damper for adjusting of said adjustable flowcross section, and to said storage and processing device (8, 10) as aninput thereto.
 2. The method of claim 1, comprising the further step oftransmitting said reference damping value (Fdref) to said storage andprocessing device (8, 10) as an input thereto.
 3. The method of claim 1,comprising the further step of calculating a vehicle body velocity, saidvehicle body velocity comprising one said variable of state; saidreference damping force calculated dependent on said vehicle bodyvelocity and said actual value of said piston velocity.
 4. The method ofclaim 1, wherein said step of calculating said reference damping force(Fdref) comprises the step of utilizing a Karnopp control concept. 5.The method of claim 1, wherein said step of calculating said referencedamping force (Fdref) comprises the step of utilizing digital or analogcomputing circuitry.
 6. The method of claim 1, wherein said controlsignal comprises a control voltage, and said step of transmitting saidcontrol signal comprises transmitting said control signal to said dampervia a voltage/through-flow cross-section converter (9).
 7. The method ofclaim 6, wherein said storage and processing unit (8, 10) comprises oneof digital and analog circuitry.
 8. The method of claim 7, comprisingthe further steps of:sensing a piston travel; providing a signalrepresenting said sensed piston travel; differentiating said signalrepresenting said sensed piston travel; rectifying said differentiatedsignal with a full-wave rectifier; squaring said rectified signal; andmultiplying said squared signal with said control voltage.
 9. The methodof claim 8, comprising the further steps of:sensing a vehicle bodyvelocity; providing a signal representing said vehicle body velocity;inverting said signal representing said vehicle body velocity dependenton a mathematical sign of said actual value of said piston velocity;rectifying said inverted signal with a half wave rectifier; summing saidrectified and inverted signal with said rectified and differentiatedsignal, said summed signals representing said reference damping force.10. The method of claim 1, wherein said vehicle includes a plurality ofwheels, said at least one damper comprising a plurality of dampers, eachsaid damper respectively associated with each said wheel, each saiddamper including a suspension control circuit.
 11. The method of claim1, wherein said at least one variable of state comprises at least one ofpiston travel, piston velocity, piston acceleration, and vehicle bodyvelocity.
 12. A method for at least one of control and regulation of achassis on a vehicle, said chassis including at least one adjustabledamper having a piston and an adjustable flow cross section, said methodcomprising the steps of determining a reference damping force for saidpiston dependent on at least one variable of state, said variable ofstate including an actual value of a velocity of said piston; andadjusting said adjustable flow cross section dependent on said actualvalue of said piston velocity and a said reference damping force;wherein the improvement comprises the steps of:generating a controlsignal dependent on an actual damping force and said reference dampingforce; generating a signal representing said actual damping force in astorage and processing device (10) dependent on said actual value ofsaid piston velocity and said control signal; and adjusting saidadjustable flow cross section dependent on said control signal.
 13. Adevice for at least one of control and regulation of a chassis on avehicle, comprising at least one adjustable damper having a piston andan adjustable flow cross section, means for determining a referencedamping force for said piston dependent on at least one variable ofstate, said variable of state including an actual value of a velocity ofsaid piston; and means for adjusting said adjustable flow cross sectiondependent on said actual value of said piston velocity and a saidreference damping force; wherein the improvement comprises:means forgenerating a control signal dependent on an actual damping force andsaid reference damping force; and a storage and processing device (10)for generating a signal representing said actual damping force dependenton said actual value of said piston velocity and said control signal;said adjusting means adjusting said adjustable flow cross sectiondependent on said control signal.